Abstract
The concrete core deformation due to shrinkage and creep in concrete-filled steel tube (CFST) members has rarely been considered in current design codes and its effects on the long-term behavior of CFST members has been a challenging task because it is hard to experimentally mimic concrete shrinkage and creep in a short term. In this study, multi-scale numerical investigations are conducted to examine the interface debonding between the steel tube and concrete core induced by concrete shrinkage and creep under different loading condition. The influence of the resulting interface debonding on the structural behavior of a 34-story CFST column, consisting of a CFST column connected to four reinforced concrete (RC) frame beams through an RC ring beam at each floor level, is further evaluated. The shrinkage is simulated by cooling the concrete core, while the creep by modifying the elastic concrete strain. The interface debonding behavior of the CFST column is analyzed in three stages corresponding to dead load, live load, and concrete shrinkage (cooling), respectively. The stress redistribution between the steel tube and the concrete core in each stage is investigated. The results indicate that long-term shrinkage and creep of the concrete core have a significant impact on the interface behavior between the steel tube and concrete core in the 34-story CFST columns. The characteristics of interface debonding at different regions of the structure are significantly different. When the shrinkage strain is 1.0 × 10−4, the steel tube and concrete core can deform compatibly with some interface debonding. As the shrinkage strain exceeds this value, pronounced interface debonding and relative slip develop, accompanied by substantial local deformation of the steel tube, under sustained axial loading. These findings reveal that time-dependent deformation of the concrete core can markedly alter the interaction between steel tube and concrete core, highlighting the necessity of considering long-term shrinkage and creep effects in the design of CFST columns to ensure serviceability and durability over extended period. It is suggested that further studies are required to evaluate the interface behavior of CFST structures with different joint details under different load conditions throughout the service life.